Transcript Chapter 8: Exceptions and I/O Streams Java Software Solutions Second Edition

Chapter 8: Exceptions and I/O Streams
Presentation slides for
Java Software Solutions
Foundations of Program Design
Second Edition
by John Lewis and William Loftus
Java Software Solutions is published by Addison-Wesley
Presentation slides are copyright 2000 by John Lewis and William Loftus. All rights reserved.
Instructors using the textbook may use and modify these slides for pedagogical purposes.
I/O Streams

A stream is a sequence of bytes that flow from a source to a
destination

In a program, we read information from an input stream
and write information to an output stream

A program can manage multiple streams at a time

The java.io package contains many classes that allow us to
define various streams with specific characteristics
I/O Stream Categories

The classes in the I/O package divide input and output
streams into other categories

An I/O stream is either a
• character stream, which deals with text data
• byte stream, which deal with byte data

An I/O stream is also either a
• data stream, which acts as either a source or destination
• processing stream, which alters or manages information in the
stream
Standard I/O

There are three standard I/O streams:
• standard input – defined by System.in
• standard output – defined by System.out
• standard error – defined by System.err

We use System.out when we execute println
statements

System.in is declared to be a generic InputStream
reference, and therefore usually must be mapped to a more
useful stream with specific characteristics
The Keyboard Class

The Keyboard class was written by the authors of your
textbook to facilitate reading data from standard input

Now we can examine the processing of the Keyboard class
in more detail

The Keyboard class:
•
•
•
•
•
declares a useful standard input stream
handles exceptions that may be thrown
parses input lines into separate values
converts input stings into the expected type
handles conversion problems
The Standard Input Stream

The Keyboard class declares the following input stream:
InputStreamReader isr =
new InputStreamReader (System.in)
BufferedReader stdin = new BufferedReader (isr);

The InputStreamReader object converts the original
byte stream into a character stream

The BufferedReader object allows us to use the
readLine method to get an entire line of input
Text Files

Information can be read from and written to text files by
declaring and using the correct I/O streams

The FileReader class represents an input file containing
character data


See Inventory.java (page 397)
See InventoryItem.java (page 400)

The FileWriter class represents a text output file

See TestData.java (page 402)
Object Serialization

Object serialization is the act of saving an object, and its
current state, so that it can be used again in another
program

The idea that an object can “live” beyond the program that
created it is called persistence

Object serialization is accomplished using the classes
ObjectOutputStream and ObjectInputStream

Serialization takes into account any other objects that are
referenced by an object being serialized, saving them too